Despite patellar resurfacing, symptoms referable to the patella femoral joint are still a major reason for complaints after total knee arthroplasty. Up to 40% of patients undergoing total knee arthroplasty have anterior knee or retropatellar pain in the postoperative period. Reoperation for patella femoral symptoms constitutes a large percentage of revisions of total knee arthroplasties. Despite the magnitude of this problem no correlation has been made with knee function or implant position. Most studies have dealt only with major technical errors that have led to patella fracture, lateral subluxation or dislocation of the patella. Patellar fractures following wide lateral retinacular release and/or massive patellar resection may in part be related to a vascular insult. Patellar subluxation, abnormal tracking or dislocation is most often associated with inadequate balance or rotational malalignment of the tibial component. These problems, however, account for only a small percentage of all patella femoral complaints and are not as widespread as the vague, aching pain or mechanical symptoms that are most commonly identified in the postoperative period.
The focus in total knee arthroplasty is to insure correct rotational, anterior/posterior and varus/valgus positioning of the implant as well as to insure soft tissue balance. Anterior/posterior and varus/valgus stability are the primary concerns. Only after all components are positioned can one check the position of the patella. However, there are several technical errors in an otherwise technically well aligned prosthesis that can lead to poor balance of the patella femoral joint. First, the choice of femoral component that is either too small in the anterior/posterior position or alternately too anteriorly placed will result in a large flexion gap. To balance this gap in extension an excess of distal femur must be removed.
These gaps are usually filled with a thick tibial component. This results in a functional shortening of the patellar ligament with its attendant increase in symptoms as discovered herein. Other theoretical technical errors include a relative medial position of the tibial and femoral components or lateral positioning of the patellar component which could increase the lateral patellar pressure syndrome. If the patella subluxes laterally or if the patella femoral pressure is too great a surgeon has very few options. The first is a lateral retinacular release. The lateral release has its own problems as well as being a relatively poor solution for an iatrogenic shortening or lengthening of the patellar ligament. Another alternative is lateralization of the components of the total knee arthroplasty. While this is attractive from a patellar femoral tracking standpoint, it will increase the varus moment during single leg stance. There is no data discussing potential benefits from lateralization or risks of aseptic loosening from an asymmetric positioning of the prosthesis. The final alternative is a major distal realignment including elevating or transferring the tibial tubercle or Z-lengthening of the patellar ligament. A bony procedure places the fixation of the tibial component at risk and lengthening puts the ligament at risk. Both may slow the rehabilitative procedure substantially.